Electron discharge device



Aug. 10, 1948. p, p DERBY 2,446,531

ELECTRON DISCHARGE DEVICE Filed May 21, 1945 TUNING CONTROL Patented Aug. 10, 1948 UNITED STATES PATENT" OFF-ICE nLEc'rRoN DISCHARGE DEVICE Palmer I. Derby, Boston, Mass, assignor to Ray- .theon Manufacturing Company, Newton, Mass.,

a corporation of Delaware Application May 21, 1945, Serial No. 594,841

5-Claims.

My present invention relates to electron-discharge devices, and more particularly to tunable electron-discharge devices.

My present invention is especially suitable for tuning or modulating electron-discharge devices adapted to generate electrical oscillations having a wave length of the order of a few centimeters or less, for example, devices-of the so-called magnetron type.

While not limited thereto,.I prefer that such a'device comprise a centra1ly-disposed cathode structure, an anode structure spaced from and surrounding said cathode structure, and incorporating one or more cavity resonators, and means for establishing a magnetic field in a direction transversely of the electron-path between said cathode and anode structures.

When a proper voltage is applied between the cathode and anode structures of such a device, and the magnetic field thereof is adjusted to an appropriate value with respect to the electric field created by said voltage, electrical oscillations are generated of a Wave length determined by theeinductance and capacitance built into the device'as a function, primarily,-of the geometry of the physical elements making up the aforementioned cavity resonators.

As stated in a copending application of mine, entitled Electron discharge device, Serial Number 591,029, filed April 30, 1945, I have found that by introducing a stream of electrons into one or more of such cavity resonators and, through the use of vcoacting magnetic and electric fields, causing .said electrons to take orbital rather than straight-line pathstherein, I am 'able to-obtain considerable deviation from the natural resonant frequency of the device. I believe that this is :due-to the change in the dielectric constant of the space within the cavity resonators, brought about by the charge of said electrons. In said copending application, the source of said electrons is an electron-gun which introduces the electrons in the form of a relatively narrow beam.

I have found, however, that with such a gun, the

frequency deviation obtainable, while considerable,-is not, for some purposes, sufficient.

It is, therefore, the main object of my present invention to provide an electron source for use in electronically tuning a device of the general character indicated which enables the attain ment of greater frequency deviation than has heretofore been possible.

It is a further object of my present inventionto provide an electron source for theabove-described expensive to manufacture.

These and other objects of my present invention, which will become more apparent as the detailed description thereof progresses, are attained, briefly, in the following manner:

.Instead of employing an electron-gun for building up the space charge in the cavity resonator, as disclosed in my copending application, I mount a cathode therein, said ,ca-thode being provided with an elongated electron-emissive surface adapted to produce an electronstream having awidth whichis substantially .co-

extensive with the length of the cavity resonator.

By means of such --a cathode, aegreater space charge is obtainable, and, therefore, a greater control over the dielectric constant of the resonator s-pacc.

I surroundsaid cathode with-a sheath having a longitudinal split therein to permit egress of the emitted electrons, and by controlling the intensity of an electric field established between said sheath and said cathode, Iam able to control the density of the electron-stream introduced into the resonator.

In addi-tion, I mount an anode insaid resonator, said-anode being spaced from the cathode and having an appropriate potential between itself. and the cathode, whereby the emitted electrons are captured and prevented from falling upon the walls of the cavity resonator.

In the accompanying specification. I shall de scribe, and in the annexed drawing show, an, illustrative embodiment of the electron-discharge device of my present invention. It is, however,- to be clearly understood that I donot wish to be limited to the details herein shown and described for the purposes of illustration only,.inasmuch as changes therein may be made without the exercise-of invention .and within the true spirit and scope of the claims hereto appended.

Insaid drawing:

Fig. 1 is a fragmentary, longitudinal sectional View of atunable electron-discharge device made in accordance with the principles of my present invention; and

Fig. 2 is a fragmentary, perspective view of .one of the cavity resonators of such an electron-discharge device, showing the disposition thereinrof theelectronic tuning means of my present .i'nvention.

Referring now more in detail to the aforesaid illustrative embodiment of 'my present invention, and with particular reference to the draw, ing illustrating the same, .thenumeral 5 ,gen-.

erally designates an electron-discharge device of the so-called magnetron type.

As herein shown, said device includes an anode structure 6, a cathode structure I, magnetic means 8 for establishing a magnetic field in a direction perpendicular to the electron-path between said cathode and anode structures, and tuning means 9. i

The anode structure 6 preferably comprises a cylindrical body l0, made of highly conductive material, such as copper, and provided with a plurality of anode members in the form of the interiorly-extending, radially-disposed vanes H.

The cylindrical body Ill is closed at its ends by plates I2 and IS, the junctions between said body and said plates being hermetically sealed, as at l4.

The cylindrical body In is of such diameter, and the number, size, and relative spacing of the vanes H are so chosen that each pair of adjacent vanes, together with that portion of said cylindrical body lying therebetween, defines a cavity resonator at the unaltered frequency desired of the output of the device.

- The cathode structure 1, which is coaxial with the anode structure 6, preferably comprises an elongated sleeve 5, conventionally made of nickel or the like, and having a reduced portion l6 which is substantially coextensive with the vertical dimension of the vanes in'other words, with thelength of the cavity resonators, and provided with a highly electron-emissive coating IT, for example, of the well known alkaline-earth metal oxide type.

In order to support the cathode sleeve i with respect to the anode members H, said sleeve may be reduced at its lower end Hi to fit into a tubular conducting member I9, the latter, in turn, being insulatedly supported, in: any desired manner (not shown), by a tubular pole piece 20 hermetically sealed, as at 2|, into the end plate l2, said pole piece being provided with a bore 22 through which the cathode structure may enter the device.

The cathode sleeve l5 may be heated by a filament 23 connected at one end 24 to said sleeve, and at the other end 25 to a lead-in conductor 26 suitably entering the device through the tubular conducting member l9. Current may be conveyed to the filament 23 by connecting the member l9, through a conductor 21, to the negative terminal of an appropriate source of voltage 28, and connecting the lead-in conductor 26, through a conductor 29, to a positive tap on said voltage source. The positive terminal of said voltage source may be grounded, as shown, as may be the cylindrical body In, whereby a potential difference is established between the cathode structure 1 and the anode structure 6.

Another pole piece 30 is hermetically sealed, as as 3|, into the end plate |3, said pole piece, and the pole piece 20, being fixed, for example, at the opposite ends of a horseshoe magnet (not shown) the two pole pieces and the horseshoe magnet constituting the above referred to'magnetic means 8 for establishing a magnetic field transversely of the electron-path between the cathode and anode structures of the device. 7

While not essential, I prefer that the vanes H be provided, in both the upper and lower edges thereof, adjacent their inner ends, with slots 32 receptive of two pairs of concentric conducting straps 33 and 3 4, and 35 and 36, the straps of each pair thereof alternately contacting successive vanes It has been found that when alternate 4 vanes are electrically interconnected, as by the straps just described, the tendency of the device to generate spurious oscillations, which would reduce its eificiency, is eliminated.

In the device as thus far described, there is no means for controlling the frequency thereof, and in order to provide such means, I prefer to proceed as follows:

A pipe 31 is threaded and hermetically sealed in the cylindrical body In at a point midway between any two of the vanes said pipe having a glass seal 38 fused into its outer end, and said glass seal having embedded therein three lead-in conductors 39, 40 and 4|. The lead-in conductor 39 is connected to one end of a heating filament (not shown) enclosed within a fiat, rectangular cathode member 42 which is disposed, adjacent the cylindrical body l0, within the cavity resonator defined by the anode members between which the pipe 3,! enters the device, the other end of said heating filament being electrically connected to the inner surface of said cathode memher which, in turn, is electrically connected to the lead-in conductor 40.

In order to convey current to the heating filament within the cathode member 42, the lead-in conductor 48 may be connected, through a conductor 43 to ground, and the lead-in conductor 39 may be connected, through a conductor 44, to a positive tap on a suitable source of voltage 45, the circuit being completed by grounding a negative tap on said voltage source, through a conductor 45.

The length of the cathode member 42 is substantially coextensive with that of the cavity resonator in which it is disposed, and its outer surface, facing the cathode structure I, is provided with a highly electron-emissive coating 41.

By the means just described, a stream of electrons having a width substantially coextensive with the length of the cavity resonator in which the cathode 42 is located, is introduced into said cavity resonator and, if desired, additional cathodes may be incorporated into the device to introduce similar electron-streams into additional cavity resonators.

I prefer that the electrons so introduced be captured before they fall onto the vanes II, and,

for this purpose, I provide a collecting electrode 48 which enters the device through a glass seal 49, the latter being fused into a pipe 5|! which is threaded and hermetically sealed into the end plate IS. The electrode 48 extends into the cavity resonator and is located closely adjacent the outer straps 33 and 35, and it is connected, through a current-limiting resistor 5|, and a conductor 52, to the positive terminal of the voltage source 45, the potential to which said electrode is thereby raised being higher than that of the anode structure 6.

The electron path between the cathode 42 and the collecting electrode 48 is, it will be noted, transverse of the magnetic field, more particularly, the leakage field, between the pole pieces 20 and 30. It is also transverse of the radiofrequency field between the vanes I l of the cavity resonator. Hence, by adjusting the intensity of said leakage field so that the orbital frequency of the emitted electrons is slightly difierent, either lower or higher than the frequency of said radio-frequency field, a space charge of appreciable density can be built up throughout a considerable region of the cavity resonator, and maximum tuning eifect can be obtained.

I surround the cathode member 42 with a metallic sheath 53 provided with a longitudinal slot 54 in its wall adjacent the coated surface of said cathode member, said sheath being connected to the lead-in conductor M; and by connecting the latter, through conductors 55 and 5B and any suitable source 51 of tuning control signal, to the negative terminal of the voltage source 45, the space charge density in the above referred to cavity resonator can be varied so as to tune or modulate the device.

It is preferable that alternating current be kept out of the voltage source 45, and, for this purpose, a by-pass capacitor 58 may be connected between ground and the negative terminal of said voltage source.

In order to extract power from the device, I provide a loop 59 which may be introduced into any one of the cavity resonators defined by the anode structure 6, said loop entering said device through a glass seal (not shown) fused into a pipe 50 threaded and hermetically sealed into the cylindrical body ID.

This completes the description of the aforesaid illustrative embodiment of my present invention. It will be noted from all of the foregoing that I have provided a simple and inexpensive electronic tuning means for an electron-discharge device of the so-called magnetron type, said tuning means enabling greater frequency deviation than it has heretofore been possible to obtain, for example, by the means disclosed in my copend'ing application identified in the earlier portions of this specification.

Other advantages of my present invention will readily occur to those skilled in the art to which the same relates.

What is claimed is:

1. An electron-discharge device comprising a cathode; an anode structure spaced from said cathode and incorporating a. cavity resonator; means adjacent said anode structure for establishing a magnetic field through said cavity resonator; electron-emissive means disposed in said cavity resonator for introducing therein an electron-stream having a width substantially coextensive with the length of said cavity resonator; means adjacent said electron-emissive means for controlling the density of said electron-stream; and means, spaced from said electron-emissive means, for collecting the emitted electrons.

2. An electron-discharge device comprising a cathode; an anode structure spaced from said cathode and incorporating a cavity resonator; means adjacent said anode structure for establishing a magnetic field through said cavity resonator; a cathode, provided with an elongated, electron-emissive surface, disposed in said cavity resonator for introducing therein an electronstream having a width substantially coextensive with the length of said cavity resonator; means adjacent said cathode for controlling the density or said electron-st eam; and means, paced om said cathode, for collecting the emitted electrons.

3. An electron-discharge device comprising a cathode; an anode structure spaced from said cathode and incorporating a cavity resonator; means adjacent said anode structure for establishing a magnetic field through said cavity resonator; a cathode, provided with an elongated, electron-emissive surface, disposed in said cavity resonator for introducing therein an electronstream having a width substantially coextensive with the length of said cavity resonator; a split sheath surrounding said cathode, and adapted to have an electric field established between itself and said cathode for controlling the density of said electron-stream; and means, spaced from said cathode, for collecting the emitted electrons.

4. An electron-discharge device comprising a cathode; an anode structure spaced from said cathode and incorporating a cavity resonator; means adjacent said anode structure for establishing a. magnetic field through said cavity resonator; a cathode, provided with an elongated, eleotron-emissive surface, disposed in said cavity resonator for introducing therein an electronstream having a width substantially coextensive with the length of said cavity resonator; means adjacent said cathode for controlling the density of said electron-stream; and an electrode, spaced from said cathode, and adapted to have an electric field established between itself and said cathode, for collecting the emitted electrons.

5. An electron-discharge device comprising a cathode; an anode structure spaced from said cathode and incorporating a cavity resonator; means adjacent said anode structure for establishing a magnetic field through said cavity resonator; a cathode, provided with an elongated, electron-emissive surface, disposed in said cavity resonator for introducing therein an electronstream having a width substantially coextensive with the length of said cavity resonator; a split sheath surrounding said cathode, and adapted to have an electric field established between itself and said cathode, for controlling the density of said electron-stream; and an electrode, spaced from said cathode, and adapted to have an electric field established between itself and said cathode, for collecting the emitted electrons.

PALMER P. DERBY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,241,976 Blewett et a1. May 13, 1941 FOREIGN PATENTS Number Country Date 114,102 Australia Oct. 22, 1941 

